In such automatic exchanges it is known to provide routing modules, e.g. in the form of orthogonal switching matrices, responsive to instructions from associated control units which in turn may be commanded by a central controller. As a given switching matrix serves only a limited number of peripheral units, the several matrices must be able to intercommunicate in order to establish signal paths between stations respectively served thereby. This creates problems when the network must be expanded to accomodate additional subscribers and/or to provide for a greater variety of available services.